1. Field of the Invention
This invention relates to fasteners, especially fasteners suitable for use in mounting panels or sheets of metal, plastics or composition materials to supporting structures and/or to each other. Such fasteners are commonly used in the construction of metal buildings and the like. Fasteners according to the present invention have special utility and advantages in attaching plastic sheet or corrugated panels, for example, such as is used for connecting a skylight to a supporting structure. Such fasteners can be mounted where access to only one side of a panel is possible, so-called "blind fasteners".
2. Brief Description of the Prior Art
Heretofore, various fasteners have been developed for use in mounting panels of sheet metal, plastics or composition materials to supporting structures and/or to each other. One such fastener which has gained acceptance commercially for plastic sheet and the like is sold by the assignee of this application under the trademark "Lap-Lox". The Lap-Lox fastener comprises an aluminum or stainless bolt positioned within a composite metal-neoprene bonded washer and extending through a grommet having an internally bonded threaded brass insert. As the bolt is turned in the insert, the grommet is compressed and it collapses against the side laps. This fastener has limited clamp-up capability and resistance to tensile forces.
Another fastener sold under the trademark "Fab-Lok" is made entirely of metal material and is primarily intended for fastening metal sheets together or to heavy or light gauge framing. As shown in U.S. Pat. No. 3,667,346, it comprises a tubular sleeve which has a head on one end for bearing against one side of the work or panel to be mounted and an internally threaded tail portion on the opposite end. A metal screw which is threaded throughout its entire length is extended through the head and sleeve into the tail and is positioned so that the screw head is normally initially spaced from the head of the sleeve. The shank of the sleeve is slotted and the resulting strips are notched internally at about the midpoint between the ends of the shank so that by turning the screw the tail portion travels toward the head and the strips are folded against the other side of the work or panel to be mounted. Since the fastener has both a metal sleeve and a metal screw, in practice it has been necessary to provide a neoprene rubber or similar material washer between the head of the sleeve and the work to effect a seal therebetween to prevent leakage at the point of mounting.
In addition, since the screw is threaded throughout its entire length in the Fab-Lok fastener, as the tail portion travels toward the head portion when the screw is turned, there is a danger of overtorquing, thus stripping the external threads on the screw or the internal threads in the tail portion, loosening or destroying the otherwise secure connection between the work and the fastener.
Thus, it would be desirable to provide an improved fastener for mounting panels or sheets of metal, plastics or composition materials to supporting structures and/or to each other under circumstances where both sides or only one side of the work is accessible to the installer. It would also be desirable for such fasteners to be lightweight, inexpensive and to have improved corrosion resistance, and to incorporate means to prevent overtorquing of the fastener so that a tight, moisture-free connection would be virtually guaranteed upon proper installation. The fastener must also have a clamp-up capability and ample resistance to tensile forces.
Prior fasteners have included means for preventing or reducing corrosion and for preventing overtorquing. For example, U.S. Pat. No. 3,343,442 discloses a fastener which includes a resilient sleeve of an elastomeric material, for example polyurethane rubber, which is molded over the head of a metal bolt. As a nut is tightened onto the bolt threads the sleeve is compressed tightly, which is said to effectively seal the aperture in a panel on which it is mounted. The shank of the bolt of the disclosed fastener has a narrow unthreaded neck portion intermediate the ends of the bolt. According to the patent, the nut can only be torqued onto the bolt until it reaches the narrow neck portion, at which point application of additional torque will only cause the nut to spin freely. It will be appreciated, however, that such a fastener requires a separate molding operation to effect a bond between the sleeve and the bolt head. It also requires available access to both sides of the work so that the nut can be tightened. Moreover, the expandable sleeve extends from the outside surface of the work when the fastener is installed, whereas it is desirable, as in the "Fab-Lok" fastener, that the expandable portion of the fastener be hidden from view behind the panel, especially in installations where the outside surface is "finished" and the panel is attached to supporting structures.
Means for preventing overtorquing of a screw and tubular sleeve fastener in the form of an expansion anchor bolt is disclosed in U.S. Pat. No. 3,316,796. The fastener disclosed in that patent includes a bolt having a shank with a diametrically reduced portion intermediate the ends of the shank. The bolt is installed in the sleeve and tightened to pull the end of the sleeve toward the head of the bolt. When the reduced portion of the bolt is reached, according to the patent the bolt will rotate within the thread aperture at the end of the sleeve but the end will not move any further toward the opposite or head end of the sleeve.
The present invention has distinct advantages over each of the foregoing known fasteners, as will become apparent from a perusal of the present specification.